There are known brake control systems (cf., e.g., U.S. Pat. No. 3,588,189; Cl.303-21) comprising a master brake cylinder, a hydraulic fluid pressure modulator with a vacuum responsive actuator, a wheel brake cylinder, a wheel rotational speed pickup transducer, a motor vehicle speed transducer, a control unit, a source of vacuum (engine), and an electromagnetic valve, wherein braking moment is controlled by energy generated by the engine of a motor vehicle.
Apart from being structurally complicated, the frequency of operating cycles in such systems is not sufficiently high.
There is also known a controllable pumping means intended to increase the volume of a hydraulic fluid in an anti-lock brake system for bringing down the braking pressure. The pumping means is driven by the engine of a motor vehicle through a cam and a follower roller, which takes off some power from the engine and extends its operating time at unstable operating conditions (cf., British Pat. No. 1,493,674; IPC B60T 8/093, published 1977).
A skid control device is further known to comprise a hydraulic fluid pressure modulator driven by a reversible electric motor thereby making it necessary to accommodate in a motor vehicle an additional drive means resulting in additional engine loading and structural complication of the system (cf. U.S. Pat. No. 3,420,580; Cl. 303-21).
Suspension of a motor vehicle may include an air compression system (cf. U.S. Pat. No. 3,688,859) in the form of a cylinder, the housing of which is affixed to the vehicle frame, while a piston rod of the cylinder is attached to a wheel suspension member of the vehicle. On the one hand, this enables to utilize vertical travel of the vehicle wheel suspension members as a source of power for air pressurization. On the other hand, such an arrangement is disadvantageous in that utilization of the energy produced by the wheel suspension members affects performance thereof and results in a less smooth travel of the motor vehicle.
There is also known a mechancial wheel anti-lock means (cf. U.S. Pat. No. 3,651,900; IPC B60T 8/16, published 1971) comprising master and wheel brake cylinders, and an additional smaller cylinder having two oppositely disposed pistons therein. Due to the fact that a brake disk is made up of two annular working parts having disposed therebetween circumferentially thereof four spokes of substantially rectangular cross-section, modulation of pressure of the hydraulic fluid in the wheel brake cylinder is effected by virtue of variations in the rigid connection between the brake disk and a hub. Such a mechanical overcomplication of the wheel anti-lock means reduces to a great extent its reliability.
An attempt has been made to utilize the energy of the transmission of a motor vehicle for driving a variable displacement pumping means (cf. U.S. Pat. No. 4,082,369; Cl. 303-3; and British Pat. No. 1,248,787; IPC B60T 8/08). However, such systems are inherently disadvantageous because the pumping means is driven by the transmission in the driving mode of operation which in the end leads to additional loading of the engine.
Finally, there is known a hydraulically operated anti-lock brake system (cf. British Pat. No. 1,227,950; IPC B60T 8/08, published 1971) which is closest to the one to be described later in this specification. It comprises a master brake cylinder connected to a wheel brake cylinder through an electromagnetic valve, two hydraulic fluid tanks, two pumping units powered by a cam drive means from a transmission, and a control unit for controlling the action of the electromagnetic valve, the control unit being connected to a wheel rotational speed transducer or sensor. An alternative embodiment of the anti-lock brake system according to the above-cited patent comprises a master brake cylinder connected to a wheel brake cylinder via an electromagnetic valve, a hydraulic fluid tank, a pumping means driven by a cam drive powered from the transmission, a control unit for controlling the function of the electromagnetic valve, the control unit being connected to a wheel rotational speed sensor. This system is likewise disadvantageous because it requires the use of a large number of parts which reduces the overall reliability thereof.